Self-contained transformer and low voltage lamp



g- 1970 P. c. DIMITRACOPOULOS ET AL 3,525,012

SELF-CONTAINED TRANSFORMER AND LOW VOLTAGE LAMP Filed Sept. 25, 1967United States Patent T US. Cl. 315-70 1 Claim ABSTRACT OF THE DISCLOSUREAn illumination source converting electric energy to light. Acombination of a power transformer and an electric lamp, the secondarywinding of the transformer being a part of the light-emitting filamentand lying wholly within the lamp, thereby eliminating the leads andcontacts which usually connect an electric lamp to its source ofelectric energy.

FIELD OF INVENTION This invention relates to electric projection lamps,i.c. to lamps used to provide the illumination source of projectors.

DESCRIPTION OF PRIOR ART It is well known that electric incandescentlamps radiate light when an electric current passes through, and therebyheats, their filament. It is also well known that the higher thetemperature of the filament, the greater the illumination efliciency.Unfortunately, it is not possible to exceed certain temperatures withoutmelting or sublimating these filaments, and therefore by keeping theirtem peratures at a relatively lower value, the major part of theelectric energy is converted into unwanted heat. This is a doubly costlyprocess, not only because of the resulting low light efiiciency, butalso because of the bulky, heavy and expensive mechanisms that must beprovided (such as motor driven blowers) to circulate the air around suchlamps and thus avoid excessive heat buildnps, which, in turn, will burnthe filaments or melt the lamps and other parts and components mountedor located near them.

It is evident that the heavier the filament (i.e. the greater itsdiameter) the better it will withstand higher temperatures. Filamentsare made today mainly from refractory metals, such as tungsten, eachhaving a certain specific resistivity. It follows that, for a givenillumination, the voltage, the filament diameter and its length must beproperly adjusted. In order to have a short filament (and thusapproximate a point-source of light which is very often ideally suitedfor projectors), the voltage must be lowered. In order to withstandgreater heating, the filament must be heavy. But the mains power line isusual ly 110 volts (or up to 220 volts in some countries), andtherefore, lamps had to be built for these voltages, which meant fineand long filaments, which in turn were burning fast and did notapproximate a point source of light.

Another approach was the so-called low voltage 3,525,012 Patented Aug.18, 1970 lamps, usually about 12 or 24 volts. Although this lowervoltage is still not sufficiently low, they necessitate quite heavy andbulky transformers, having approximately the weight and size of theblowers and motors that they are supposed to eliminate. Thus, no netgain was possible.

As mentioned briefly above, even 12 or 24 volt operation is still abovethe desired values. However, there are limitations as to how low thisvoltage can be dropped: For low voltage, high intensity applications,the amperage becomes excessive, necessitating heavy connecting leadsthat must pass through the glass envelope of the lamp and this causesconsiderable sealing problems.

It is evident that the low voltage winding of the transformer must alsobe of substantially heavy wire and the connecting leads from thetransformer to the lamp must also be quite heavy.

OBJECTS OF THE INVENTION It is the object of this invention to provide anovel and unique combination of low voltage lamp and transformer, boththe lamp and the transformer forming one single integrated unit.

It is a further object of this invention to provide suchlamp-transformer combination that totally eliminates the connectingleads from the secondary of the transformer to the lamp socket.

It is a further object of this invention to provide such alamp-transformer combination whereby the secondary of the transformerforms part of, and is enclosed inside, the projection lamp.

It is a further object of the present invention to pro vide suchlamp-transformer combination, which totally eliminates any and all leadsleading from the filament socket pins and/or socket contacts, andthereby eliminates the sealing problems.

It is a further object of the present invention to provide suchlamp-transformer combination, which due to its special configuration andattributes, makes possible a low wattage, long life, high temperatureand high efficiency filament, which may, if desired, approximate a pointsource of light, or alternatively, have a desired size and shape.

It is a further object of the present invention to provide such alamp-transformer combination, fed with electric alternating current ofhigher than the mains frequency, and/ or chopped portions or suchalternating frequency, thereby substantially reducing the size andweight of the transformer primary and transformer iron core.

Other objects of the invention will become evident from the ensuingdescription, illustration and claim.

SUMMARY The invention achieves its objectives and solves a large part ofthe problems above-described by providing a lamp whose filament, or asuitable part of such filament, constitutes the secondary winding of apower transformer, such secondary winding being wholly within, orforming a part of, the lamp itself, which lamp is preferablydoughnut-shaped and may surround the transformer primary or thetransformers iron core.

3 This transformer-lamp combination feeds the lightemitting portion ofthe filament with as low a voltage as desired, and since the power tothe filament is inductively transferred, it does not require the usualheavy connecting wires and contacts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view taken alongline 1-1 of FIG. 2.

FIG. 2 is a somewhat simplified view of a preferred em-- bodiment of theinvention.

FIG. 3 is a partly sectional, side elevation view of another preferredembodiment of the present invention. FIG. 4 is a sectional view alongline 4-4 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now bedescribed by reference to certain preferred specific embodimentsthereof, however, it will be understood that the principles of theinvention can be carried out by specifically different physical means,and furthermore, in using words of limited meaning, for the betterunderstanding of the particular types and embodiments chosen fordescription and illustration, it is not intended to exclude variationsof those details, which properly fall within the scope of the inventionor claims.

As previously stated, the present invention solves the bulk, weight,leads, sealing and other problems associated with the usual type ofprojection lamps and their associated power supplies. This is achievedby combining the secondary of a power transformer with the filamentleads of the lamp itself.

Referring to the accompanying illustrations, 5 and 5 designate the(usually laminated) iron core of a transformer, while 7 is the bobbincontaining the primary transformer winding 9.

The low voltage secondary of the transformer is designated by numerals11 and 13, and forms a complete loop or circle around the transformercore 5 and 5. Part 11 of this loop or circle is of heavy metallicconstruction, for example a copper wire, while 13 is the filamentitself, which may be of tungsten, as is the usual practice today, orother appropriate material. By means of spacers or supports, for exampleceramic or mica support plates 17, this secondary loop is held andproperly positioned within a glass or quartz envelope 15. In otherwords, the transparent lamp envelope is doughnut-shaped and envelops oneleg of the transformer, while the filament and is metallic supportconstitute the low voltage secondary of the transformer. In this way,the pins or connectors, usually attached on the socke of the projectionlamp are totally eliminated, as are the leads passing through the glassor quartz envelope connecting these pins or contacts to the filament.The usual leads connecting these pins or contacts to the power supplyare also eliminated, and thus this transformer-lamp combination makespossible the construction of lamps feeding their filament not only withsay 12 volts, but even a small fraction of a volt.

It is well known that:

(l) W: V R or Watts: (Volts) Ohms For higher illumination, it isnecessary to pass through the filament as many watts as it is practical,while at the same time, the largest possible percentage of these wattsmust be converted to light and not unwanted heat. But it must not beforgotten that this is achieved by raising the filament temperature tothe highest possible temperature before this high temperature melts orsublimates it. Of course, the larger the diameter of this filament thegreater its mechanical strength at a given temperature, but making afilament large in diameter and small in length (for a given wattagedissipation) may only be done, according to the above Formula 1, if thevoltage is dropped substantially (since the watts are proportionate tothe square of the volts).

It can now readily be seen how this novel lamp permits the feeding ofthe filament 13 with extremely low voltage, without the associatedproblems connected with high intensity currents, since:

A reflecting mirror 21 may also be inserted within the lamp envelope, inthe usual fashion, or the glass or quartz envelope may be shaped in theproper fashion, just behind the filament, and metalized in order to actas a reflecting mirror, as it is well known in the art. It is evidentthat this mirror may also be placed outside the glass or quartzenvelope, and supported on the transformer core or other appropriate anddesired support.

The transformer core may be built in two distinct parts, each beingsubstantially L-shaped, as shown in FIG. 1, part 5 may be hingedlysupported on part 5, for example by means of pin 23 or other suitablemethod. In this fashion, by lifting member 5 in the direction of arrowA, it is possible to withdraw, insert, or replace the doughnut-shapedlamp.

Obviously, other equally suited methods may be employed to open thetransformer core in order to remove the lamp.

The usual means power frequency is 60 cycles per second in the Americancontinent and usually 50 cycles per second in Europe and other parts ofthe world. At these frequencies, in order to arrive at a suflicientlyhigh inductive coupling between the transformer primary and secondarywindings and thus obtain an acceptable transformer efiiciency, it isnecessary to wind these windings around a fairly substantial amount ofiron core. This iron core adds to the bulk and weight of thetransformer, which of course, is a most unwanted feature. Fortunately,the higher the current frequency, the lower the amount of iron core, andafter a certain frequency level, the coupling of the windings may beachieved without the interposition of any iron core. It is therefore anadvantage to increase the mains frequency to a higher level and therebygreatly reduce the iron core, weight and bulk.

When higher frequencies are employed as above described, especially whenthe looped iron core is not essential, a configuration substantially asthat illustrated in FIGS. 3 and 4 is indicated. Numerals indicatingvarious parts are the same used in the preceding description, inconnection with FIGS. 1 and 2. The primary 9 may be optionally split intwo, and the transparent envelope 15, containing the secondary winding,i.e. lead 11 and illuminating element 13, may be placed between its twoparts, as shown in these FIGS. 3 and 4. In FIG. 3, for illustrativepurposes, one part of the transformer primary winding is shown in a sideelevation view, while the other part and the transparent envelope withits enclosed secondary winding (lead 11 and illuminating element 13)have been shown in a sectional view.

If the power frequency warrants it, the center core 25 may be made ofany suitable, magnetically permeable, material, such as sintered orpowdered iron, etc., in order to achieve a better magnetic couplingbetween the windings.

In the above introduction and description it is repeatedly stated orimplied that these novel lamps are particularly well suited asillumination sources for projectors and the like. While this is so, itmust be made clear that the invention is equally well suited and may beequally well used not only in connection with projectors, but for anyand all applications requiring an illumination source, including, ofcourse, any and all lamp applications, like illumination of rooms,streets, etc., etc.

The invention has been described by reference to certain preferredspecific embodiments thereof, however, it will be understood that theprinciples of the invention can be carried out by specifically differentphysical means, and furthermore, in using words of limited meaning, forthe better understanding of the particular types and embodiments chosenfor description and illustration, it is V=I x R or Volts=Amperes Ohmsnot intended to exclude variations of those details, which properly fallwithin the scope of the invention or claim.

What is claimed is:

1. An electric illumination source comprising a high frequency electricvoltage transformer at least a part of Whose secondary windingconstitutes the light producing element, comprising a bobbin-shapedtransformer primary winding and an annular secondary winding totallyenclosed within a substantially annular transparent envelope, a smallportion of said secondary winding consituting the light emittingelement, said primary winding and secondary winding being substantiallycoaxially superimposed upon one another and being electromagneticallycoupled to one another.

References Cited UNITED STATES PATENTS JAMES W. LAWRENCE, PrimaryExaminer 10 C. R. CAMPBELL, Assistant Examiner U.S. Cl. X.R.

